Method of synchronizing.



C. A. LOHR.

METHOD OF SYNCHRONIZING.

APPLICATION FILED MAY27. 19oz.

Patented Nov. 7, 1916.

INVENTOR Q d. M

WITNESSES.

CARL A. LOHR, OF NEW YORK, N. Y.

METHOD OF SYNCHRONIZING.

Specification of Letters Patent.

Patented Nov. '7, 1916.

Application filed May 27, 1907. Serial No. 376,021.

electrically connected with the alternatingcurrent circuit. Suchmachines therefore can be of the induction-type, differing from theordinary asynchronous induction-motor (or generator) only therein, thatboth machine-members are in electrical connection with thealternating-current circuit. I have called these machines synchronousinduction motors (or generators) and this termis used herein, to definethese machines. Furthermore the class of machines referred to includesthe different types of synchronous electric machines, in which therotarypart is in electrical connection with the circuit by means of acommutator or rectifying-device, such as all the different types ofsynchronous self-exciting generators or synchronous self-excitingmotors.

When using machines of the inductlon type as synchronous motors, thestarting up to a speed, which is equal or nearly equal to thesynchronous speed can be efiected by different means, as described andclaimed in different applications for a patent, filed by me. My presentinvention is independent of the method, which is employed for startingsuch motors up to their synchronous speed, but contemplates a method,after the starting of the motor has been accomplished, to define theproper relative angular position between the two motor-members, which isfixed by the regular synchronous speed, at which the motor is intendedto be operated.

The synchronous induction motor more particularly, when brought. up toor nearly to the synchronous speed, which is obtained by electricallyconnecting both members of the motor with the alternating-currentcircuit, can then be connected in the proper way, so as to operatesynchronously and will often immediately assume the exact synchronous,speed, and therewith the n'oper relative angular position of the twomotormembers, which is determined and maintained by the synchronism. Formost purposes however it is necessary to exactly determine the moment ofsyncln'miimn,

fore making the connections to regularly operate the motor or generatorat the 1ntended synchronous speed. Although. when properly connected up,the motor or generator will generally have a tendency to assume itssynchronous speed and therewith the proper angular position, whenrunning at a speed, which is nearly equal to the synchronous speed, itmay happen, that in the moment of making the connections for thesynchronous speed the motor or generator is in an unfavorable angularpositiomn'hich will cause a momentary rush of the current taken from thealternating-current circuit or even an absolute short-circuit in casethe windings of stator and rotor are in a relative'position to destroytheir fields.

With regard to the angular position of rotor and stator in the moment ofimpressing the Voltage of the supply-circuit upon the windings of bothmotor-members, three different cases are possible, viz: First case. Thepoles produced in one member are exactly facing opposite poles of theother member; the motor will then represent a maximum of self-induction.Second case. The poles produced in one member are eX- actly facing equalpoles of the other memher; the motor will then represent a mini mum ofself-induction. Third case. The poles produced in the two motor-membersarein a position intermediate between the positionsof the first and thesecond case; the motor will then represent a self-induction, of amagnitude lying between the maximum of the first case and the minimum ofthe second case. a

The first case gives the most favorable condition for a synchronousoperation of the motor, the connections for a synchronous operationtherefore should be made in the moment of the occurrence of the firstcase, The motor then will take up not more current, than when runningunder no load. Also in case the starting-device of the motor I iscapable to start the motor under a part of its load or under full load,the motor will not take more current from the alternating currentcircuit, than is corresponding to the load actually carried by themotor.

The second case will cause the two fields in stator and rotor to be inopposition, thus the motor will ofier very little self-induction, andaccordingly take up a considerable current, when connected so as tooperate synchronously. The most unfavorable condition for synchronizingis therefore found in the moment of the occurrence of the second case.

The third case is often more or less equivalent to the first or to thesecond case, and the connections for a synchronous operation can be madewithout any obnoxious effect, when the third case is approaching thefirst case.

The object of my present invention is to determine, which of the threecases is present, when the synchronizing of the motor is intended, andmore specially to determine the moment of the occurrence of the firstcase, in order to make the connections for the synchronous speed in themost favorable moment.

In carrying out my invention, I arrange the synchronous induction motoror generator and the necessary devices in accordance with theaccompanying drawing, of which Figure 1 shows my invention applied to asynchronous induction motor, having stator and rotor-windings connectedin series, while Fig. 2 shows the application of my invention to such amotor, having stator and rotor-windings connected in parallel.

Fig. 1 more particularly shows the mains l of an alternating-currentcircuit (threephase), an alternating-current motor 2, having alternatingcurrent windings on both of its members. The windings of the rotor 8 ofthis motor are connected over collectorrings and brushes, as shown, inseries with the windings of the stator l, and the windings of the stator4 are properly connected by means of the conductors 5 and the mainswitch6 with the mains of the alternatingcurrent circuit. Thus when switch 6is closed, and the motor is brought up to its synchronous speed, themotor will operate as synchronous induction motor. As the method ofstarting the synchronous induction motor is independent of my presentinvention, I have shown the synchronous induction motor as being startedby a special small motor 7 by means of the pulley 8, belt 9 and pulley10. The motor 7 may be a motor of any kind and has the only purpose tostart the synchronous induction motor up to a speed, which is aboutequal, or also somewhat higheror lower than the synchronous speed of themotor 2. The operation of determining the occurrence of the first caseand the most favorable moment for closing the main switch and runningthe motor with its regular synchronous speed from thealternating-current circuit is carried out as follows: I impress a partof the supplyvoltage upon one phase (the corresponding phase) of themotor, said part for instance being obtained by tapping an inductiveresistance 11, which is connected by means of the conductors 12 with oneof the phases of the alternating-current mains 1, and furthermore tappedby the conductors 13, which are connected over the switch 14, whenclosed, with the conductors 5 and 5 which supply the correspondingphases of the windings of both members of the motor, when operating assynchronous induction motor. Inserted in the conductors 13 is anampere-meter 15, which indicates the current taken up by the motor, whenrunning nearly at synchronous speed and when offering different amountsof self-induction in different momentary angular positions. Thereforeevery change in the relative angular position of the motor-members willmanifest itself in the ampere-meter 15 as a corresponding change of thecurrent taken up by the motor. More particularly the proper momentaryangular position, which is most favorable for a synchronous operation ofthe motor (first case, maximum selfinduction) will manifest itself by aminimum value shown by the ampere-meter, while the most unfavorableposition (second case, minimum self-induction) will be indicated by amaximum value shown by the ampere-meter. Also an intermediate momentaryangular position (third case) will be indicated by an intermediateposition of the ampere-meter, viz., the ampere-meter will show a valuebetween said minimum and maximum values, which are indicated during theoccurrence of the first and second case respectively.

The dilferent amounts of self-induction represented by the motor in itsdifferent momentary angular positions, can equally well be indicated bya voltmeter 16, which is connected over the conductors l7 and switch 18with another phase of the motorwindings for instance with the phasebetween the conductors 5 and 5. The windings of the motor, to which thevoltmeter is connected, are with regard to the windings, to which thevoltage is impressed, in a relation similar to the secondary and primarywindings of a transformer, therefore the electromotive forces induced inthe windings between the conductors 5 and 5 will be in proportion to themagnetic field-strength of the field produced in the motor, but not tothe amount of current taken from the circuit and shown in theampere-meter. It is therefore obvious, that the voltmeter can equallywell as the ampere-meter be used to indicate the most favorablemomentary position of the motor-members by a maximum voltage set up inthe windings between the conductors 5" and 5. Either one of the twoinstruments, the ampere-meter 15 as well as the voltmeter 16 can be usedto determine the proper moment, in which the motor can be synchronouslyoperated by the alternating-current circuit. In practice therefore onlyone of the instruments is necessary to obtain a synchronizing of themotor, it may however be of advantage, to use both instruments as shownin the drawing.

The operation of the motor in brief is as follows: The motor is broughtup to a speed, which is in the neighborhood. of the synchronous speed,which is intended to be produced by simultaneously connecting bothmotor-members with the alternating-current circuit. Then a small part ofthe supplyvoltage is impressed upon the motor-windings by closing theswitch 1 1. The speed at which the motor is running may be practicallyequal to the synchronous speed, but will always be such as to slightlydiffer therefrom, and to produce successively the first, second andthird case. Switch 18 may be closed simultaneously with switch let inorder to operate the voltmeter 16. The instruments l5 and 16 will thenindicate in synchronism with the occurrence of the first, second andthird case in the motor a minimum, maximum or intermediate value ofcurrent and a maximum, minimum or inter mediate value of voltagerespectively. The proper moment for synchronously operating the motor istherefore indicated by either one of the instruments 15 or 16, by theampere meter 15, when showing a minimum current and by the voltmeter 16,when showing a maximum voltage. The regular synchronous working of themotor can then be effected by closing the main-switch 6. Before orsimultaneously with the closing of the switch 6 the switches 1 1 and 18should be opened, in order to prevent the instruments from beingoperated by the regular supply-voltage of the mains 1.

In practice the arrangement of the devices as shown in the drawing maybe more or less changed, without departing from the spirit of myinvention. For instance the instruments 15 and 16 need not be regularampere and voltmeters, which are capable of showing the current and thevoltage in amperes and volts respectively, as for the purpose of myinvention it is only of interest to indicate the moment of minimumcurrent and maximum voltage. Also these instruments for instance may bereplaced by incandescent lamps, which show the proper conditions bytheir greater or less brilliancy. Furthermore when using instruments themoment which is best adapted to produce the synchronous speed, can bedetermined by a practical trial, and the proper position of theinstruments can then be fixed by a mark, which is put on the scale ofthe instruments.

Also forcertain cases it may be more advantageous, to produce thesynchronous op-. eration of the motor not exactly in the moment which isindicated by the instruments or their equivalent devices by a maximum orminimum value, but somewhat earlier or later, which also may be bestdetermined by a practical test. I

In Fig. 2 I have shown the same arrangement for a synchronous inductionmotor, the rotor and stator circuits of which are in parallel. and themode of operation is exactly the same as shown and described for Fig. 1.

Also in Fig. 2 the same letters as in Fig. 1 are used for the samedevices. In Fig. 2 more specially the rotor-windings are paral leledwith the stator windings by means of the conductors 19, which join theconductors 5 as shown in the drawing. The phases of the stator as wellas the phases of the rotorwindings are connected in delta and theconnection of the rotor-winding with the conductors 19 especially aremade by means of collector-rings and brushes as shown.

While in the foregoing description and accompanying drawing thesynchronous machine is intended to be operated as synchronous motor, Iwish to be understood, that it may equally well be employed as agenerator. In this case naturally there is no differencein thearrangement of the devices; the motor 7 only would then indicate theprimemover, by which the generator 2 is driven.

While I have shown herein and particularly described some embodiments ofmy invention, I do not wish to limit myself to the precise arrangementsas herein shown, since many modifications can be made without departingfrom the spirit of my invention.

Having thus described my invention, I claim as newand desire to secureby Letters Patent 1. The new art or" synchronizing, which consists inimpressing a part of the voltage of a current source on a dynamo whennear synchronism, and applying the full voltage or said source at aninstant of a critical inductive reaction of said dynamo.

2. The new art of synchronizing a dy The arrangement of the devices thesource, and supplying normal operating current to said dynamo at aninstant which is characterized by a critical inductive behavior of saiddynamo when preliminarily connected. I

3. Themethod of synchronizing a dynamo with a current source, whichconsists in exciting both members of said dynamo similarly to normalsynchronous operation from a part of the voltage of the source forproducing a relatively weak field in either member, and normallyconnecting said dytion in a moment where said fields are adding eachother.

a. The method of synchronizing a synchronous dynamo with respect to agiven current source, which consists in rotating said dynamo nearsynchronism, supplying both members of said dynamo when so rotating withcurrent oi a value considerably less than that of the normal operatingcurrent for the purpose of determining an in stant which is favorablefor proper synchronous operation, and supplying the normal operatingcurrent to said dynamo at or approximately at said instant.

5. The method oi synchronizing a dynamo with a given.alternating-current source, which consists in impressing a comparativelysmall part of the voltage upon said dynamo when rotating in proximity tosynchronism, and establishing the normal connections for synchronousoperation at an instant which is characterized by a critical value ofself-induction of said dynamo.

6. The method of synchronizing a dynamo with an alternating-currentsource, which consists in first establishing connections between saiddynamo and a comparatively small part of the voltage of said source,said connections being similar to those for normal synchronousoperation, and connectin said dynamo normally to said source at theinstant when the self-induction of said dynamo reaches a certaincritical value.

7. The method of synchronizing a dynamo with an alternating-currentsource, which consists in establishing preliminary connections betweensaid dynamo and a part of the voltage of said source, and normallyconnecting said dynamo, when in proximity to synchronism, to said sourceat the instant, when a maximum value of field strength is developed insaid dynamo by said preliminary connections.

8. The method of synchronizing a dynamo with an alternating-currentsource, which consists in establishing preliminary connections betweensaid dynamo and a comparatively small part of the voltage of saidsource, indicating the variable field strength thus developed in saiddynamo when in proximity to synchronism, and normally connecting saidsource to said dynamo at the instant when a critical value of said fieldstrength is developed in said dynamo.

9. The method of synchronizing a synchronous electric machine withrespect to an alternating-current circuit, which consists in bringingsaid machine to a speed which is in proximity to synchronism, impressinga small part of the voltage of said alternatingcurrent circuit upon saidmachine, indicating the varying value of the self-induction of saidmachine, and connecting said machine to said alternating-current circuitat the instant when its self-induction reaches a certain critical value.

10. The method of synchronizing a synchronous electric machine of theinduction type with an alternating-current circuit, which consists inbringing said machine to a speed which is in proximity to synchronism,impressing a part of the voltage of said alternating-current circuitupon both members of said machine, indicating the varying amount of theself-induction of said machine, and connecting said nnachine for normalsynchronous operation in or approximately in the moment when thewindings of said machine have a certain critical value ofself-induction.

11. The method of syi'ichronizing a synchronous electric machine of theinduction type with an alternating-current circuit, which consists inimpressing a small part of the voltage of said alternating-currentcircuit upon both members of said machine, indicating the varying amountof self-induction of said machine when running in proximity tosynchronism, and connecting said machine to said alternating-currentcircuit for normal synchronous operation at or approximately at theinstant when said machine has a maximum value of self-induction.

In testimony whereof I have affixed my signature in presence of twowitnesses.

CARL A. LOHR.

Witnesses G. S. MALTHA, RAY MORRIS.

Copies of this patent may be obtained for five cents each. by addressingthe Commissioner of Patents, Washington, D. C.

